1. Field of the Invention
The present invention relates to information handling systems and more particularly to an image processor for producing antialiased images.
2. Description of the Related Art
There are a number of different types of aliasing effects which appear in images. Staircase aliasing is the effect which can be observed on lines and edges which are at an angle to the horizontal and vertical directions on a pixel-based display such as a raster-scanned visual display device or a matrix printer. This invention is directed to reducing staircase aliasing and does not specifically address other aliasing problems such as the Moire patterns associated with sampling aliasing.
Antialiasing is a technique which reduces this effect as perceived when viewing the displayed image by adjusting the intensity of the displayed pixels along the line or edge. It has been proposed to perform antialiasing at various times and in various ways during the generation of the images for display.
Where an image is the result of some rendering process, such as the creation of two-dimensional views of a three-dimensional object in a solid modeling system, the antialiasing can be performed on each edge or line as it is generated. Antialiasing in this manner can be termed prefiltering. This can be performed by a technique termed "supersampling", where extra values are calculated and then averaged. This and other prefiltering approaches, are, however, expensive in terms of processing time.
It has also been suggested to perform antialiasing after an image has been created by convolution filtering. Antialiasing after an image has been created can be termed postfiltering. This technique has the disadvantage, however, of blurring the image too much with the result that even horizontal and vertical lines become blurred.
There is a need, therefore, for another approach to the antialiasing of images which is not as expensive as prefiltering, yet produces better results than convolution filtering. The object of the invention is to fulfill this need.